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Looks like SQ's A359s have fuel dumping capability but Finnair's don't. Is this a customer option, or is there something else going on?

Yup, it's optional:



Full source (warning, 389 page PDF): http://www.smartcockpit.com/docs/a350-9 ... pilots.pdf

My best guess is that airlines decide whether or not to equip the system based on the longest routes they use the aircraft on. The longer the routes, the more fuel they have onboard upon takeoff, the greater the need for a nozzle, should SHTF right after takeoff.

Finnair might have decided that their A359 would be able to sustain an overweight landing, in case they need to return straight away.

IIRC, BA don't have a jettison system on their A350-1000 either.

Zak wrote:My best guess is that airlines decide whether or not to equip the system based on the longest routes they use the aircraft on. The longer the routes, the more fuel they have onboard upon takeoff, the greater the need for a nozzle, should SHTF right after takeoff.

Pretty much. There's a set of calculations available to each customer airline that work out the risk and cost factors with each optional safety feature. They're not always a precise science and are occasionally proven wrong - HX had trouble with one of their A359s that was not fitted with fuel dumping and spent 4 hours flying circles over the South China Sea when an emergency meant they had to return early into a HKG-SFO run.

Zak wrote:IIRC, BA don't have a jettison system on their A350-1000 either.

Definitely not needed. BA don't send their A35X beyond about 70% of their range so they rarely take off at >105% of the MLW of the triple bogey variant.

An immediate return is not the only reason to have a fuel dumping capability. Terrain enroute factors in as well. If the fuel jettison system is on MEL, you have to look at not only the performance limit for a go around to land, but at the high terrain enroute to make sure you have the capability to remain above it if you lose an engine. If not, you would have to designate driftdown alternates and routes to those alternates. Not something ordinarily calculated for an aircraft with an operational fuel jettison system. If you don't have it period then you always have to figure in the single engine driftdown capability.